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SESK: Stuff Everyone Should Know · sesk.info/tech-recursion-base-case

In a recursive function, what is the base case?

The simple case solved directly, without calling itself again, so the recursion stops.

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  1. The first line of the function
  2. The case answered without another recursive call ✔
  3. The biggest input it can handle

Why: A recursive function solves a big problem by calling itself on a smaller one. The base case, like a list of one item already being sorted, is where it stops shrinking and just answers.

Huh, didn't know that: Merge sort's base case is a list of one item, which is already sorted by definition.

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To understand recursion, you must first understand recursion.
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References

Answer: The case answered without another recursive call. A recursive function solves a big problem by calling itself on a smaller one. The base case, like a list of one item already being sorted, is where it stops shrinking and just answers.

  1. MIT 6.006 Introduction to Algorithms, Lecture 3: Sorting ocw.mit.edu/courses/6-006-introduction-to-algorithms-spring-2020/resources/mit6_006s20_lec3
    Base case: for n = 1, array has one element so is sorted
    Checked 2026-10-10.

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